It's remembered as a day chilled by "a Siberian wind knifing down Pennsylvania Avenue" and illuminated by "the dazzling combination of bright sunshine and deep snow."

On Jan. 20, 1961, John F. Kennedy began his presidency with a speech at once soaring and solemn. Fifty years on, we have not heard an inaugural address like it. Tethered to its time and place, it still challenges with its ambition to harness realism to idealism, patriotism to service, national interest to universal aspiration.

Theodore Sorensen, the speech's principal architect, was always modest about his own role, less so about the inaugural itself. "It certainly was not as good as Lincoln's second or FDR's first," Sorensen wrote in his memoir, adding that Kennedy thought it not as good as Jefferson's first.

By acknowledging what their joint product was not, Kennedy and Sorensen defined the historical company it still keeps....